Abstract
Ecologists are increasingly interested in plant–pollinator networks that synthesize in a single object the species and the interactions linking them within their ecological context. Numerous indices have been developed to describe the structural properties and resilience of these networks, but currently, these indices are calculated for a network resolved to the species level, thus preventing the full exploitation of numerous datasets with a lower taxonomic resolution. Here, we used datasets from the literature to study whether taxonomic resolution has an impact on the properties of plant–pollinator networks.For a set of 41 plant–pollinator networks from the literature, we calculated nine network index values at three different taxonomic resolutions: species, genus, and family. We used nine common indices assessing the structural properties or resilience of networks: nestedness (estimated using the nestedness index based on overlap and decreasing fill [NODF], weighted NODF, discrepancy [BR], and spectral radius [SR]), connectance, modularity, robustness to species loss, motifs frequencies, and normalized degree.We observed that modifying the taxonomic resolution of these networks significantly changes the absolute values of the indices that describe their properties, except for the spectral radius and robustness. After the standardization of indices measuring nestedness with the Z‐score, three indices—NODF, BR, and SR for binary matrices—are not significantly different at different taxonomic resolutions. Finally, the relative values of all indices are strongly conserved at different taxonomic resolutions.We conclude that it is possible to meaningfully estimate the properties of plant–pollinator interaction networks with a taxonomic resolution lower than the species level. We would advise using either the SR or robustness on untransformed data, or the NODF, discrepancy, or SR (for weighted networks only) on Z‐scores. Additionally, connectance and modularity can be compared between low taxonomic resolution networks using the rank instead of the absolute values.
Highlights
The study of species interactions has always been central in ecology
Using plant–pollinator interaction networks from the literature, we showed that modifying the taxonomic resolution of these networks significantly changes the absolute values of the indices that describe their properties, except for two indices, namely the SR and robustness to species loss
We observed for both NODF and BR that the absolute values of these indices, but not the associated Z-scores, are strongly modified by the change in taxonomic resolution. This result is in agreement with the work of Almeida-Neto et al (2008) who showed that NODF and BR are markedly affected by the matrix fill, a parameter that is modified when the taxonomic resolution is changed
Summary
The study of species interactions has always been central in ecology. Such interactions have historically been examined by focusing on two interacting species, but in recent years, the marked increase in the amount of biological information available and the development of novel approaches and tools have placed a new focus on the study of interaction networks (Proulx, Promislow, & Phillips, 2005). Other frequently examined structural characteristics of mutualistic networks are connectance, the proportion of realized interactions among all possible ones, and modularity, that is, the extent to which linked interactions between pollinators and plants are organized into delimited modules, as well as motifs, which are subnetworks representing the interactions between a given number of taxa (Milo et al, 2002). These properties have been associated with the ecosystem's resilience to perturbations (Soares, Ferreira, & Lopes, 2017). We showed that among the set of 41 networks, the relative value of a given network for a given index is well conserved across different taxonomic resolutions, between the species and genus levels
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